Gas-driven hydraulic power converting pump

ABSTRACT

A free piston pump using a resilient pressurized gas for driving a liquid pump. The pump is a double cylinder type with the cylinders operating out of phase with each cylinder including two opposed pistons of different areas and driven in the power stroke by a gas supply pressure and returned by springs. A common control valve is connected to and simultaneously controls both cylinders by admitting gas to and between the larger area pistons and thereby actuating the smaller area pistons, coupled thereto, for pumping liquid. An arrangement is provided to cushion the pistons and control valve spool.

United States Patent Marsh et al. 4 1 Mar. 14, 1972 [54] GAS-DRIVEN HYDRAULIC POWER 3,182,895 5/1965 Panhard ..4l7/340 CONVERTING PUMP 1,813,763 7/1931 Price ..l23/43 X 2,942,553 6/1960 Moeller et al.. .....9ll308 X {721 lnvenwrsl Dav"! Mmsh, rs"? Falls- Ohm; 3,082,749 3/1963 Coberly ..91/3os x Prabhakar B. R. Koo, Muncie, Ind. [73] Assignee: Borg-Wilmer Corporation, Chicago, Ill. Primary Exami"e' Rbert f [22] Fl d M 16 1970 Attorney-Donald W. Banner and Wlham S. McCurry 1 e ar. 211 App]. No.: 19,893 [571 ABSTRACT A free piston pump using a resilient pressurized gas for driving 52 us. 0 ..417/340 417/397 91/308 a quid Pump- The Pump is a cylmde type with [51] Int Cl F04, 31/00 F04b 131/00 4 35/00 cylinders operating out of phase with each cylinder including 7 F0 25/02 two opposed pistons of different areas and driven in the power 581 Field of Search ..417/339 340 397- 91/501 Smke by a gas Supply pessum rammed A 91/308 4 412 92/50 70 common control valve is connected to and simultaneously controls both cylinders by admitting gas to and between the [56] References Cited larger area pistons and thereby actuating the smaller area pistons, coupled thereto, for pumping liquid. An arrangement UNlTED STATES P T is provided to cushion the pistons and control valve spool. 3,145,660 8/1964 Bush ..4l7/34O X 16 Claims, 7 Drawing Figurei 13 M2 7 s2 2 1 35 1e 1 4 sp 1 2T 16' 2e 22' a; v 39 l 3' c 41 gs 47 46 c2 v34 3'1 5 M1 W 25 1 22 1 31 c2 26 24 4 LE 6 E N o [:1 wow/1.11:. FLUIDHICM PRESSURE nor (5- m-razmzomrs PRESSURE m HYDQAULIC FLUID-LOW 9125551125 [:1 GAS CUSl-HQN 1:} 1-10'1' GAS-HIGH masseuse I: VENT PRESSURE {I} nor GAS-EXHAUST 911125511125 Patented March 14, 1972 3,649,135

5' Sheets-Sheet 5 INLET HYDRAULIC HYDRAUUC HYDRAULE FLUID use GAS-DRIVEN HYDRAULIC POWER CONVERTING PUMP BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates to gas-driven hydraulic power converting pumps and more particularly to a pump of this type preferably, but not necessarily, for use as an auxiliary power supply in guided missiles.

Many guided missiles require auxiliary power systems to provide missile control and to operate several missile mechanisms during missile flight. Existing auxiliary power systems employ hydraulic pumps powered by turbines with the turbine pump assembly having complicated high speed rotating components, gears and lubrication arrangements, and complex speed controls. Also, turbo-pumps are relatively heavy, require special tooling and equipment, have gyroscopic effects, and are expensive to manufacture.

Alternate auxiliary power systems have been proposed in the form of gas-driven reciprocating piston hydraulic pumps operated by power from a gas source such as the primary propulsion gas generator of the missile or an auxiliary gas generator. Pumps of this type have numerous advantages over turbopumps when evaluated on the basis of simplicity, weight, reliability, cost, performance, ready adaptability in applications and design changes and maintenance. Various types of gas-driven hydraulic pumps include a single, single-acting piston, which is not acceptable for high power space applications, as it produces power only in one direction and then must return before another stroke. Another type of pump has a single, double-acting piston producing power in both directions but it must stop travel in one direction, reverse and then compress hydraulic fluid in the cylinder before fluid delivery can restart, thus having an unacceptable hydraulic pressure drop in output at the end of each stroke. Another type of presently favored gasdriven hydraulic pump employs two moving pistons and is designed to provide for the return stroke of each piston being quicker than the power stroke so that the other piston is ready to take up the load as the expiring piston completes its stroke. For this purpose, a control valve for directing and exhausting gas to and from the cylinders must be bistable and be tripped as a function of piston motion, and an interlock must be provided to coordinate motion of the valve with motion of the pistons. In this respect, a lost motion arrangement is needed to allow the valve to shift from one end of its travel to the other end, independent of piston travel and the moving piston must hit the stationary valve to accomplish the shift with consequent metal-to-metal shock and pounding. In one example of this type of pump, a two cylinder, four piston arrangement is provided having an hydraulic piston and gas piston in each cylinder with the gas pistons actuating the associated hydraulic piston, and having gas control valves to direct high pressure gases alternately to the separate cylinders to actuate the hydraulic pistons to produce hydraulic fluid pressure and to provide constant fluid output.

It is the principal object of the invention to provide an improved gas-driven hydraulic power converting pump.

Another object of the invention is to provide an improved gas-driven hydraulic pump having double cylinders and two pistons in each cylinder having opposed motion to cancel reaction forces on the pump mounting.

Another object of the invention is to provide an improved gas-driven hydraulic pump having two power cylinders arranged to be operated out of phase to provide smooth flow of hydraulic power by pistons in the cylinders and to minimize pressure drop at the end of each power stroke.

Another object of the invention is to provide an improved gas-driven hydraulic pump having a power cylinder, and opposed pistons in the cylinder having their movement toward each other cushioned by gas trapped between the pistons.

Another object of the invention is to provide an improved gas-driven hydraulic pump having a power cylinder and opposed pistons in the cylinder simultaneously driven by an expanding gas introduced between the pistons to actuate the pistons.

Another object of the invention is to provide an improved gas-driven hydraulic pump having a power cylinder, pistons in the cylinder, a control valve for directing gas under pressure between the pistons, and means for cushioning the power stroke of the pistons in the cylinder by employment of a piston-position sensing line which is opened, upon approach of the pistons to the limit of the power stroke, to shift the control valve to prevent further inlet gas flow.

Another object of the invention is to provide an improved gas-driven hydraulic pump having a power cylinder, pistons in the cylinder, a valve for controlling the flow of gas under pressure to the cylinder, and means for gas cushioning the valve to prevent the valve striking its housing.

Another object of the invention is to provide an improved gas-driven hydraulic pump having a power cylinder, pistons in the cylinder, a linearly movable valve for controlling the flow of gas under pressure to the cylinder, and an auxiliary valve serving to bias the control valve to prevent the control valve being disposed in a dead center position.

Further objects and advantages of the present invention will become apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of the gas-driven hydraulic pump embodying the present invention;

FIG. 2 is a schematic view of the gas control valve of the pump and illustrating its position prior to starting the pump;

FIG. 3 is a schematic view of the gas control valve of the pump and illustrating its position after starting the pump;

FIGS. 4-7 are views of the gas-driven hydraulic pump, the pump components and pump control valve being shown in section and the fluid distribution means being schematically represented to illustrate the sequence of operations of the pump.

in the drawings, there is shown a duplex pump, generally designated by the numeral 10, having a pump body provided with two cylinders 11 and 12 closed by end caps 13 and 14 secured to radially extending flanges 16 and 17 of the cylin' ders, the cylinders receiving two identical double-acting pump units P1 and P2. The pump unit Pl includes a master piston M1 and a slave piston S1. Also, the pump unit P2 includes a master piston M2 and a slave piston S2. Since the piston MI and piston S2 of the pump units P1 and P2 and the piston M2 and piston S1 are identical only the pistons M1 and S1 will be described in detail. To better emphasize the similarity between the pump units, the same numerals as are used to identify the parts of pistons M1 and S1 of unit P1 are used to identify the same or corresponding parts of M2 and S2 of the unit P2 except that such numerals are followed by a prime mark for the unit P2 in the detailed description of the pump.

The pump unit Pl has its slave piston S1 provided with head portions 17 and 18, the head portion 17 being received in the bore of and slidably engaging the cylinder 11 and the head portion 18 of smaller diameter being received in a cylinder 19 axially aligned with the cylinder 11 and having a radially extending annular flange 20 secured by screws 21 to the end cap 13. Similarly, the master piston M1 has head portions 22 and 23 of stepped diameter, with the head portion 22 being positioned within the bore of cylinder 11 and slidably engaging the cylinder, the stepped portion 23 being slidably engaged with a cylinder 24 having a radially extending flange 25 secured to the end cap 14. The pistons M1 and S1 divide the cylinders ll, 19 and 24 into a central motor chamber 26, and pumping chambers 27 and 28, respectively. Springs 29 and 30 are disposed in the cylinder 11 with the spring 29 being seated against flange 20 of cylinder 19 and engaging the head portion 17 of piston S1, and spring 30 seating on flange 25 of cylinder 24 and engaging head portion 22 of piston M1, the springs being operative to urge the pistons M1 and 51 toward each other. It will be noted that the diameter of the piston head portions 17 and 22 exceeds the diameter of the piston head portions 18 and 23 so that the pressure in the pumping chambers 27 and 28 will be substantially greater than the pressure in the motor chamber 26.

The pumping chambers 27 and 27' are connected by passages to one-way inlet check valves 31 and 32 having their inlet sides connected by a conduit C1 to a suitable source of supply of hydraulic fluid. The check valves 31 and 32 comprise a pair of valve members 34 and 35 having their aligned stems slidably mounted in the end cap 13, the head of the valve member 34, urged by a spring 36, engaging an annular seat 37, defining an opening in the end cap 13, providing a conduit C2 between the conduit C1 and pumping chamber 27; and the head of valve member 35, adapted to be urged by a spring 38, to engage annular seat 39, defining an opening in the end cap 13, providing a conduit C3 between the conduit C1 and pumping chamber 27.

As shown in FIG. 1, motion of piston M2 towards the right is being accomplished by means of spring 29' thereby increasing the volume and decreasing the pressure in chamber 27. When the pressure in chamber 27' decreases below the pressure in conduit C1, valve member 35 is disengaged from valve seat 39 against the biasing action of spring 38 and fluid enters chamber 27. At this time, the head of valve member 34 is engaged with seat 37 by means of spring 36 and pressure in passage C2; also, motion of piston S2 towards the left occurs so that fluid enters chambers 28' and 27' concurrently. Conduit C16, shown on FIGS. 4-7, delivers the fluid to chamber 28' via conduits C3 and C5.

The pumping chambers 28 and 28 are connected by passages C4 and C to the one-way discharge check valves 40 and 41, respectively controlling flow of hydraulic fluid from the chambers 28 and 28' of the piston M1 and piston S2 to an outlet passage C6. The valves 40 and 41 have their heads 43 and 44 engaged by a spring 45 acting to urge the heads toward engagement with seats 46 and 47 defined by annular openings in end cap 14 connecting outlet passage C6 with C4 and C5 and thereby chambers 28 and 28. The valves are guided for movement relative to each other, by hydraulic fluid and the spring 45, by the stems of the valves slidably positioned in axially aligned guideways in the end cap 14.

Referring to FIGS. 4-7 illustrating schematically various operational stages of the gas-driven hydraulic pump of the present invention, gas under pressure from any suitable source, such as a solid or liquid propellant gas generator or a gas compressor, for actuating the pistons M1 and S1 of pump unit P1 and pistons M2 and S2 of pump unit P2 is supplied through a conduit C7 to a gas control valve GCV operable to direct gas to or exhaust gas from the chambers 26 and 26' of the pump units and is connected to both pump units to control them simultaneously and to provide a constant fluid output. The valve GCV is a servo-actuated valve and comprises a valve spool 50 reciprocable in a valve guide 51 and has three axially spaced lands 52, 53 and 54. The valve guide is also formed with control ports 55, 56, 57, 58, 59, 60, 61, 62 and 63. Port 56 communicates at all times with land 52, port 62 with land 54, port 55 with the left end of the valve guide 51 and port 63 with the right end of valve guide 51. The control ports 57 and 58, and 58 and 59 can communicate with groove 63 between lands 52 and 53. Control ports 59 and 60, and 60 and 61 can communicate with groove 64 between lands 53 and 54. The gas conduit C7 is connected to port 57. Gas chamber 26 of P1 is connected by conduit C8 to port 58 and by branch conduit C9 to port 62, and by branch conduit C to conduit C9, the conduit C9 having a spring-biased check valve 65 preventing flow of gas through conduit C10 from chamber 26 into conduit C9. The gas conduit C7 is also connected by branch conduit C11 to port 61. The gas chamber 26 of P2 is connected to conduit C12, which is connected to conduit C13 and thereby to port 56 of the valve guide 51. A one-way check valve 66 is positioned in conduit C12. A conduit C14 connects the chamber 26' with conduit C13 and also with port 60 of the valve guide 51 and, in the valve position as shown in FIG. 4, groove 64 of valve spool 50 connects ports 60 and 59 with the gas exhaust conduit C15. Conduits C13 and C9 have restrictions 69 and 70, functioning for a purpose to be later described.

The hydraulic fluid enters the inlet conduit Cl and can flow counterclockwise through check valve 32 and the line conduit C16 to branch conduits C3 and C5 to enter pumping chambers 27 and 28, and also through check valve 41 to the outlet or discharge conduit C6. Hydraulic fluid can also enter at inlet conduit C1 and can flow clockwise through check valve 31 and line conduit C16 to branch conduits C2 and C4 to enter pumping chambers 27 and 28, and also through check valve 40 to the discharge conduit C6.

OPERATION Referring to FIG. 4, in the position of the pump components, its control valve and check valves there shown and, summarizing, the pistons M1 and S1 of pump unit P1 are at the beginning of their power stroke. gas is admitted to P1 through piston return cushion valve 65; the springs 29' and 30' are returning pistons M2 and S2 of pump unit P2 toward each other to their initial positions; and, with reference to the gas control valve GCV, at its right end, sensing pressure from the preceding power stroke of pistons M2 and S2 of pump unit P2 is decaying after shifting the control valve spool 50 to the left, also detent pressure from C9 and pump unit P1 now holds the valve spool to the left, and gas cushion pressure in port 56 to the left of valve spool 50 is preventing pounding metal-tometal contact of spool 50 with the valve guide housing 51. More particularly, gas enters the conduit C7 and flows through port 57 into groove 63 of the valve spool 50 and through port 58 to conduit C8 to the cylinder 11 containing piston M1. Since conduit C8 is now covered by piston M1, the gas enters chamber 26 of cylinder 11 through the check valve 65 and conduit C10. As the pistons M1 and S1 start their power strokes, the gas in scavenged chamber 26' of P2 is exhausted, (by expansion and then scavenged by movement of pistons S2 and M2 by springs 29 and 30') through conduit C14, port 60, groove 64 of valve spool 50, port 59 and conduit C15. At this time, the pistons S2 and M2 are moved by springs 29 and 30 on their intake stroke so that the hydraulic fluid inlet pressure at C1 need only overcome the pressure drop in the hydraulic inlet valve 32; also, pistons S1 and M1 are on their power stroke causing the high pressure hydraulic fluid to flow in conduit C16 to close inlet check valve 31 and discharge check valve 41 and to discharge the fluid through valve 40 and conduit C6 to the load.

The gas control valve is a bistable arrangement and is tripped as a function of motion of the pistons M1, S1, M2 and 52. For this purpose, detent pressures to provide the two stable positions are furnished by sensing pressures in conduits C8 and C14. Signals to switch from one stable position to another are furnished by piston position sensing conduits C17 and C18. These conduits are located to sense completion of a power stroke and cause control valve spool 50 to shift so that the power pistons do not collide with the pump body or housing. The conduit C17 connects chamber 26 in cylinder 12 to the right end of control valve guide 51 by way of a restricting orifice 71 in control port 63, and the conduit C18 connects chamber 26 in cylinder 11 to the left end of control valve guide 51 via restricting orifice 72 in control port 55. The restricting orifices 69, 70, 71 and 72 in the conduits C13 and C9, C17 and C18 to the control valve modify the valve acceleration and deceleration rates to prevent pounding and excessive inertia forces from the valve spool 50.

Referring to FIG. 5, the operating phase of the pneumatichydraulic power converter or gas-driven hydraulic pump there shown is similar to FIG. 4 but differs therefrom and as indicated by changes in the component positions in that both pistons M1 and S1 of P1 and pistons M2 and S2 of P2 are in intermediate positions. Pistons M1 and S1 are on their power stroke prior to tripping the control valve GCV, gas is entering through both conduit C and conduit C8. Pistons M2 and S2 are on their return stroke prior to cushioning of the pistons. The gas control valve is held in its left position by detent pressure in conduit C9 and port 62 of the valve guide acting on land 54 of the valve spool 50.

Referring to FIG. 6, the illustrated operating phase discloses that the pistons M1 and SI have completed their power stroke and, by so doing, have exposed the piston position sensing conduit C18 to the high pressure gas in chamber 26 of pump unit P1 to cause a change in the position of the valve spool 50 of the control valve. At this time, the pistons M2 and S2 have completed their return stroke, and check valve 66 has closed trapping gas between the pistons to cushion the pistons and thereby prevent pounding as they return to their initial position. Switching of the gas control valve is timed to prevent pounding at the completion of the power stroke of the pistons M1 and S1. Preferably, timing is such that the pistons M2 and S2 will be idle for a few milliseconds at the maximum flow rate of the power converting pump. During this idle period, the pistons M2 and S2 will contact each other and land 75 on the wall of cylinder 12 will reposition them exactly in phase for the next power stroke. The gas cushion between pistons M2 and S2 will prevent pounding of the pistons or on the land 75'. The gas control valve is shifting, by gas pressure, from chamber 26 of pump unit Pl, flowing through conduit C18 to the left end of the valve guide port 55 through orifice 72 and being applied against the valve spool 50 to shift the spool. More particularly, signal pressure from chamber 26 overcomes the detent pressure in conduit C9 from chamber 26, as the area a in the valve control chambers is twice as large as the area b in the valve detent chambers, thus ensuring prompt switching of the valve spool. Accordingly, the detent force and the net force to shift the spool are equal in magnitude and opposite in direction. The rate of rise of signal pressure from chamber 26 is controlled by the cushion restricting orifice 72.

Referring to FIG. 7, the illustrated operating phase shows the succeeding power stroke of pistons M2 and S2 beginning in cylinder 12 as the power stroke of pistons M1 and S1 terminates in cylinder 11 and exhausting of the gas begins. Thus, in the position of the pump and valve components, FIG. 7 is one-half cycle (one cylinder stroke) out of phase with FIG. 4. As illustrated in FIG. 7, the pistons M1 and S1 of pump unit P1 are on their return stroke prior to cushioning. Gas from chamber 26 flows through conduit C8, port 58, groove 63 of spool 50, port 59, exhausts through conduit C15. The pistons M2 and S2 of pump unit P2 have started their power stroke and are exactly in phase, gas from the gas supply conduit C14 flowing as shown and being admitted through the check valve 66 in conduit C12 to the chamber 26 of the pump unit P2. The gas control valve has completed its shift to the position shown, and the signal pressure in the valve guide at the left end of spool 50 is starting to decay through orifice 72. The valve spool is held to the right by the detent pressure of the gas in C13 from chamber 26' and acting in the valve guide on the land 52 of spool 50.

It may be noted that the piston return cushion valves 65 and 66 function once during each power stroke to admit gas at the start of the stroke and trap it for cushioning purposes at the end of the stroke.

DESCRIPTION OF STARTING VALVE FOR GAS CONTROL VALVE GCV FIGS. 2 and 3 schematically illustrate a starting valve BV and its operation for starting cycling of the main control valve GCV. The valve BV functions as a start-up bias valve for the gas control valve GCV when the latter valve perchance is located in an intermediate position and thereby blocks both gas supply ports 57 and 61 so that valve spool 50 is stalled at dead center. The bias valve BV is instrumental in moving the valve spool 50 should it stop at this dead center position.

The valve BV comprises a tumbler-shaped piston 76 positioned in a chamber 77 of the pump body connecting gas supply conduit C11 to a conduit C20 which is connected to the right end of the guide chamber of the valve GCV. As seen in FIG. 2, the valve piston 76 has its upper head engaged by a spring 78 reacting against the pump body and urging the piston in a downward direction to connect C 11 and C20 to permit flow of gas into chamber 79. In FIG. 3, the valve piston 76 is shown in its raised position with the lower head of piston 76 being positioned against the body thereby preventing further flow ofgas between C11 and C20.

More particularly, and referring to FIG. 2, the valve spool 50 is shown as being stopped in dead center" and no gas under pressure can enter the valve GCV except gas entering the chamber 79 through the bias valve BV. As pressure rises in chamber 79, the valve spool 50 shifts to the left and the cycling of the power pistons MI-Sl and M2 -S2 begins in the normal and previously described fashion. Gas pressure applied to the piston 76 of the valve BV then closes the valve by movement of the piston, against force of spring 78, to the position shown in FIG. 3 so that operation of valve chamber 79 is no longer affected by the valve BV. If the valve spool 50 had been initially found slightly left of dead center, both the bias gas in chamber 79 and the supply gas entering detent chamber 80 would shift the spool 50 to the left. If the spool had stopped slightly to the right of dead center," pressure in detent chamber 81 and bias pressure in control chamber 79 might both rise at the same time and oppose each other. In this case, the valve spool 50 would remain stalled until the bias valve closed. At such time, the bias pressure would decay into piston position sensing conduit C17 and, thence out the vent manifold 82 of cylinder 12. Pressure in detent chamber 81 would then overcome the decaying bias pressure in chamber 79 and the first valve spool motion would then be to the right. Thus, normal cycling of the control valve GCV would start in event its spool stalls either toward the right or left of dead center, and the bias valve BV is only required for the exact dead center" position shown in FIG. 2. Also, it will be apparent that, as the operation of the pistons of the pump units P1 and P2 is entirely dependent upon the control valve GCV, the proper timing of each pump unit is assured and the pump units cannot get out of time."

What is claimed is:

1. A gas-driven hydraulic pump comprising a source of gas under pressure; a cylinder; a pair of opposed power pistons in said cylinder and dividing said cylinder into a motor chamber centrally of said cylinder, and liquid pumping chambers at the ends of said cylinder; conduit means connected to said pumping chambers; passage means connecting said gas pressure source to said motor chamber to simultaneously move said pistons in opposite directions in power strokes to discharge liquid in said pumping chambers through said conduit means; valve means operatively connected to said passage means for alternately connecting and disconnecting said gas pressure source and said motor chamber; biasing means for moving said pistons toward each other in return strokes to exhaust gas from said motor chamber when said valve means is operative to disconnect said gas pressure source and said motor chamber; and means controlled by one of said pistons, adjacent the limit of its power stroke, to actuate said valve means to disconnect said source and said motor chamber.

2. A gas-driven hydraulic pump as set forth in claim 1 including means connecting said motor chamber and said valve means, upon movement of said pistons to positions adjacent the limit of their power strokes, for flow of gas under pressure from said motor chamber to said valve means to move said valve means to disconnect said gas pressure source and said motor chamber.

3. A gas-driven hydraulic pump as set forth in claim I including biasing means for moving said pistons toward each other in return strokes to exhaust gas from said motor chamber when said valve means is operative to disconnect said gas pressure source and said motor chamber; and means for exhausting gas from said motor chamber and controlled by one of said pistons to terminate flow of exhaust gas from said motor chamber before said pistons reach the end of their return strokes by said biasing means.

4. A gas-driven hydraulic pump as set forth in claim 1 including biasing means for moving said pistons toward each other in return strokes to exhaust gas from said motor chamber, said passage means providing a gas inlet port in said cylinder and located centrally of said motor chamber; and means defining a port in said cylinder for exhausting gas from said cylinder when said valve means is operative to disconnect said gas pressure source from said gas inlet port, said exhaust port being axially spaced from said gas inlet port and closable by one of said pistons during movement of said pistons toward each other by said biasing means whereby gas in said motor chamber is trapped between said pistons.

5. A gas-driven hydraulic pump as set forth in claim 1 including a check valve in said passage means and operative to prevent return flow of gas from said motor chamber through said passage means, said passage means terminating in an inlet port in said cylinder and located centrally of said rotor chamber; an exhaust conduit connected to said valve means and an outlet conduit in said cylinder and axially spaced from said inlet port; a connecting conduit between said motor chamber and said valve means; and a piston position-sensing port in said cylinder and located adjacent the end of said motor chamber and providing gas under pressure in said motor chamber to said connecting conduit during power stroke movement of said pistons to actuate said valve means to connect said motor chamber to said exhaust conduit.

6. A gas-driven hydraulic pump as set forth in claim 1 in which said valve means includes a cylinder having a pair of inlet and outlet control ports connected respectively to said source and said motor chamber, and a valve spool in said valve cylinder and having a pair of lands defining a groove in said spool and movable to a first position in which said valve spool groove connects said ports and also movable to a second position in which one of said lands can block said inlet port; and a starting valve connected to said source of gas under pressure and to said valve cylinder and operative by gas under pressure to direct gas under pressure to said valve spool to move said spool from said second position to said first position.

7. A gas-driven hydraulic pump including a source of gas under pressure; a first cylinder; a first pair of opposed pistons in said first cylinder and dividing said first cylinder into a motor chamber centrally of said first cylinder, and liquid pumping chambers at the ends of said first cylinder; a second cylinder; a second pair of opposed pistons in said second cylinder and dividing said second cylinder into a motor chamber centrally of said second cylinder, and liquid pumping chambers at the ends of said second cylinder; conduit means connected to said pumping chambers; first passage means for connecting said source to each of said motor chambers to provide gas under pressure to said pistons in the motor chamber for moving said pistons away from each other to force liquid from said pumping chambers; second passage means connectable to said motor chambers for exhausting gas from said motor chambers by movement of said pistons toward each other; a valve operatively connected to said first and second passage means for controlling the alternate admission of gas to and exhaust of gas from the motor chambers of said cylinders; biasing means in each cylinder for moving said pistons therein toward each other to exhaust gas from said motor chambers; and means for operating said valve between a first position, connecting said source to said motor chamber of said first cylinder by said first passage means while connecting said second passage means to the motor chamber of said second cylinder to exhaust gas therefrom, and a second position connecting said source to said motor chamber of said second cylinder by said first passage means while connecting said second passage means to the motor chamber of said first cylinder to exhaust gas therefrom.

8. A gas-driven hydraulic pump as set forth in claim 7 in which said valve operating means is controlled by movement of said pistons.

9. A gas-driven hydraulic pump as set forth in claim 7 in which said valve operating means is controlled by movement of said pistons in said cylinders to positions adjacent the ends of their power strokes.

10. A gas-driven hydraulic pump as set forth in claim 7 in which said valve operating means includes means alternately connecting said motor chambers with said valve, upon movement of said pistons in each chamber to positions adjacent the limits of their power strokes, for flow of gas under pressure between said valve and connected motor chamber to move said valve to disconnect said source and the motor chamber.

11. A gas-driven hydraulic pump as set forth in claim 7 in which said valve operating means includes conduits between said motor chambers and opposite ends of said valve and each conduit having an inlet in the associated cylinder adjacent the end of the power stroke of one of the pistons in the cylinder, and an outlet terminating at the associated end of said valve.

12. A gas-driven hydraulic pump as set forth in claim 7 including a gas inlet port in each cylinder and located centrally of the working chamber thereof and connected to and forming a portion of said passage means; means defining a gas outlet port in each cylinder and axially spaced from said gas inlet port and closable by one of said pistons in the cylinder during movement of said pistons by said biasing means to trap gas between said pistons.

13. A gas-driven hydraulic pump as set forth in claim 7 including means for exhausting gas from each motor chamber and controlled by one of said pistons therein to terminate flow of gas from the motor chamber prior to completion of the return strokes of the pistons therein by their biasing means to trap gas between said pistons.

14. A gas-driven hydraulic pump as set forth in claim 7 in which said valve includes a valve spool reciprocal in a valve body, and said valve operating means includes a pair of conduits connecting said motor chambers to opposite ends of said valve body and each conduit having an inlet in the associated cylinder adjacent the end of the power stroke of one of the pistons in the cylinder, and an outlet terminating at the associated end of said valve body, said conduits having orifices each alternately restricting the flow of gas under pressure to said valve body to move said valve spool and also to restrict the flow of exhaust gas from said valve body by valve spool movement to modify acceleration and declaration rates of travel of said valve spool thereby to prevent the valve spool striking the ends of the valve body during shifting movement thereof.

15. A gas-driven hydraulic pump as set forth in claim 7 including a gas inlet port in each cylinder and located centrally of the motor chamber thereof, a gas outlet port in each cylinder and axially spaced from said inlet port, and a piston position sensing port in each cylinder and located adjacent the end ofeach motor chamber; and in which said valve includes a cylindrical body having spaced first and second ports connected to said gas source, a third port, a first conduit connected to said third port and having a first branch connected to said inlet port of said first cylinder, a second branch connected to said outlet port of said first cylinder, a check valve in said first branch preventing flow ofgas from said first cylinder, a fourth port, a second conduit connected to said fourth port and having a first branch connected to said inlet port of said second cylinder, a second branch connected to said outlet port of said second cylinder, a check valve in said first branch of said second conduit preventing flow of gas from said second cylinder, fifth and sixth ports at opposite ends of said valve body and respectively connected to said piston position sensing ports of said cylinders, and a valve spool in said cylindrical body having spaced lands defining first and second grooves therebetween, said valve spool being movable, by gas under pressure entering said fifth port from said piston position sensing port in said first cylinder, to a first position connecting said first port to said fourth port by said first groove of said spool to provide gas under pressure from said source to said inlet port of said second cylinder and to the motor chamber thereof while connecting said outlet port of said first cylinder to said exhaust port by said second groove to evacuate gas from said motor chamber of said first cylinder, said valve being also movable, by gas under pressure entering said sixth port from said piston position sensing port in said second cylinder, to a second position connecting said second port to said third port by said second groove of said spool to provide UNITED STATES PATENT OFFICE CERTEFICATE @F CGRREfi'HQN 3, 9, 35 Dated March 97 Patent No.

Inventor s David C. Marsh, et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 7, line 21-, "rotor" should read motor Signed and sealed this 31st day of October 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GO'ITSCHALK Attesting Officer Commissioner of Patents FORM Po-1050 (10-69) USCOMM-DC eoam pae U.S. GOVERNMKNT PRINTING OFFICE I959 O-3G6-J)4 

1. A gas-driven hydraulic pump comprising a source of gas under pressure; a cylinder; a pair of opposed power pistons in said cylinder and dividing said cylinder into a motor chamber centrally of said cylinder, and liquid pumping chambers at the ends of said cylinder; conduit means connected to said pumping chambers; passage means connecting said gas pressure source to said motor chamber to simultaneously move said pistons in opposite directions in power strokes to discharge liquid in said pumping chambers through said conduit means; valve means operatively connected to said passage means for alternately connecting and disconnecting said gas pressure source and said motor chamber; biasing means for moving said pistons toward each other in return strokes to exhaust gas from said motor chamber when said valve means is operative to disconnect said gas pressure source and said motor chamber; and means controlled by one of said pistons, adjacent the limit of its power stroke, to actuate said valve means to disconnect said source and said motor chamber.
 2. A gas-driven hydraulic pump as set forth in claim 1 including means connecting said motor chamber and said valve means, upon movement of said pistons to positions adjacent the limit of their power strokes, for flow of gas under pressure from said motor chamber to said valve means to move said valve means to disconnect said gas pressure source and said motor chamber.
 3. A gas-driven hydraulic pump as set forth in claim 1 including biasing means for moving said pistons toward each other in return strokes to exhaust gas from said motor chamber when said valve means is operative to disconnect said gas pressure source and said motor chamber; and means for exhausting gas from said motor chamber and controlled by one of said pistons to terminate flow of exhaust gas from said motor chamber before said pistons reach the end of their return strokes by said biasing means.
 4. A gas-driven hydraulic pump as set forth in claim 1 including biasing means for moving said pistons toward each other in return strokes to exhaust gas from said motor chamber, said passage means providing a gas inlet port in said cylinder and located centrally of said motor chamber; and means defining a port in said cylinder for exhausting gas from said cylinder when said valve means is operative to disconnect said gas pressure source from said gas inlet port, said exhaust port being axially spaced from said gas inlet port and closable by one of said pistons during movement of said pistons toward each other by said biasing means whereby gas in said motor chamber is trapped between said pistons.
 5. A gas-driven hydraulic pump as set forth in claim 1 including a check valve in said passage means and operative to prevent return flow of gas from said motor chamber through said passage means, said passage means terminating in an inlet port in said cylinder and locatEd centrally of said rotor chamber; an exhaust conduit connected to said valve means and an outlet conduit in said cylinder and axially spaced from said inlet port; a connecting conduit between said motor chamber and said valve means; and a piston position-sensing port in said cylinder and located adjacent the end of said motor chamber and providing gas under pressure in said motor chamber to said connecting conduit during power stroke movement of said pistons to actuate said valve means to connect said motor chamber to said exhaust conduit.
 6. A gas-driven hydraulic pump as set forth in claim 1 in which said valve means includes a cylinder having a pair of inlet and outlet control ports connected respectively to said source and said motor chamber, and a valve spool in said valve cylinder and having a pair of lands defining a groove in said spool and movable to a first position in which said valve spool groove connects said ports and also movable to a second position in which one of said lands can block said inlet port; and a starting valve connected to said source of gas under pressure and to said valve cylinder and operative by gas under pressure to direct gas under pressure to said valve spool to move said spool from said second position to said first position.
 7. A gas-driven hydraulic pump including a source of gas under pressure; a first cylinder; a first pair of opposed pistons in said first cylinder and dividing said first cylinder into a motor chamber centrally of said first cylinder, and liquid pumping chambers at the ends of said first cylinder; a second cylinder; a second pair of opposed pistons in said second cylinder and dividing said second cylinder into a motor chamber centrally of said second cylinder, and liquid pumping chambers at the ends of said second cylinder; conduit means connected to said pumping chambers; first passage means for connecting said source to each of said motor chambers to provide gas under pressure to said pistons in the motor chamber for moving said pistons away from each other to force liquid from said pumping chambers; second passage means connectible to said motor chambers for exhausting gas from said motor chambers by movement of said pistons toward each other; a valve operatively connected to said first and second passage means for controlling the alternate admission of gas to and exhaust of gas from the motor chambers of said cylinders; biasing means in each cylinder for moving said pistons therein toward each other to exhaust gas from said motor chambers; and means for operating said valve between a first position, connecting said source to said motor chamber of said first cylinder by said first passage means while connecting said second passage means to the motor chamber of said second cylinder to exhaust gas therefrom, and a second position connecting said source to said motor chamber of said second cylinder by said first passage means while connecting said second passage means to the motor chamber of said first cylinder to exhaust gas therefrom.
 8. A gas-driven hydraulic pump as set forth in claim 7 in which said valve operating means is controlled by movement of said pistons.
 9. A gas-driven hydraulic pump as set forth in claim 7 in which said valve operating means is controlled by movement of said pistons in said cylinders to positions adjacent the ends of their power strokes.
 10. A gas-driven hydraulic pump as set forth in claim 7 in which said valve operating means includes means alternately connecting said motor chambers with said valve, upon movement of said pistons in each chamber to positions adjacent the limits of their power strokes, for flow of gas under pressure between said valve and connected motor chamber to move said valve to disconnect said source and the motor chamber.
 11. A gas-driven hydraulic pump as set forth in claim 7 in which said valve operating means includes conduits between said motor chambers and opposite ends of said valve and each conduit having an inlet in the associated cylInder adjacent the end of the power stroke of one of the pistons in the cylinder, and an outlet terminating at the associated end of said valve.
 12. A gas-driven hydraulic pump as set forth in claim 7 including a gas inlet port in each cylinder and located centrally of the working chamber thereof and connected to and forming a portion of said passage means; means defining a gas outlet port in each cylinder and axially spaced from said gas inlet port and closable by one of said pistons in the cylinder during movement of said pistons by said biasing means to trap gas between said pistons.
 13. A gas-driven hydraulic pump as set forth in claim 7 including means for exhausting gas from each motor chamber and controlled by one of said pistons therein to terminate flow of gas from the motor chamber prior to completion of the return strokes of the pistons therein by their biasing means to trap gas between said pistons.
 14. A gas-driven hydraulic pump as set forth in claim 7 in which said valve includes a valve spool reciprocal in a valve body, and said valve operating means includes a pair of conduits connecting said motor chambers to opposite ends of said valve body and each conduit having an inlet in the associated cylinder adjacent the end of the power stroke of one of the pistons in the cylinder, and an outlet terminating at the associated end of said valve body, said conduits having orifices each alternately restricting the flow of gas under pressure to said valve body to move said valve spool and also to restrict the flow of exhaust gas from said valve body by valve spool movement to modify acceleration and declaration rates of travel of said valve spool thereby to prevent the valve spool striking the ends of the valve body during shifting movement thereof.
 15. A gas-driven hydraulic pump as set forth in claim 7 including a gas inlet port in each cylinder and located centrally of the motor chamber thereof, a gas outlet port in each cylinder and axially spaced from said inlet port, and a piston position sensing port in each cylinder and located adjacent the end of each motor chamber; and in which said valve includes a cylindrical body having spaced first and second ports connected to said gas source, a third port, a first conduit connected to said third port and having a first branch connected to said inlet port of said first cylinder, a second branch connected to said outlet port of said first cylinder, a check valve in said first branch preventing flow of gas from said first cylinder, a fourth port, a second conduit connected to said fourth port and having a first branch connected to said inlet port of said second cylinder, a second branch connected to said outlet port of said second cylinder, a check valve in said first branch of said second conduit preventing flow of gas from said second cylinder, fifth and sixth ports at opposite ends of said valve body and respectively connected to said piston position sensing ports of said cylinders, and a valve spool in said cylindrical body having spaced lands defining first and second grooves therebetween, said valve spool being movable, by gas under pressure entering said fifth port from said piston position sensing port in said first cylinder, to a first position connecting said first port to said fourth port by said first groove of said spool to provide gas under pressure from said source to said inlet port of said second cylinder and to the motor chamber thereof while connecting said outlet port of said first cylinder to said exhaust port by said second groove to evacuate gas from said motor chamber of said first cylinder, said valve being also movable, by gas under pressure entering said sixth port from said piston position sensing port in said second cylinder, to a second position connecting said second port to said third port by said second groove of said spool to provide gas under pressure from said source to said inlet port of said first cylinder and to the motor chamber thereof while connecting said outlet port oF said second cylinder to said exhaust port by said first groove to evacuate gas from said motor chamber of said second cylinder.
 16. A gas-driven hydraulic pump as set forth in claim 15 including conduits, between said piston position sensing ports and said fifth and sixth ports, having orifices restricting the flow of gas to said valve. 